Placing a line of typographic ornaments on page top with class memoir

Question

Based on the utilities provided by the class memoir, I'd like to set a line of typographer's ornaments along the page top of a custom size stock paper (actually, along the four page edges, but my question refers only to the top edge). In order to do so, I thought of setting the baseline of my header right at the very top of the page by declaring a 0pt head height and a 0pt head drop -- terms introduced in the class documentation --, but for some reason I end up with a distance from the top of the page to the baseline of the header which amounts to my font's declared normalsize (in the MWE below, this is 11pt). What am I doing wrong?

\documentclass[11pt]{memoir}

\usepackage{calc,pstricks}

\setstocksize{20cm}{20cm}
\settrimmedsize{\stockheight}{\stockwidth}{*}
\setlrmarginsandblock{\paperwidth * 1/10}{*}{1}
\setulmarginsandblock{4\baselineskip}{3\baselineskip}{*}  
\setheadfoot{0pt}{3\baselineskip}
\setheaderspaces{0pt}{*}{*}
\checkandfixthelayout

\setlength{\headwidth}{\paperwidth}
\makepagestyle{mainpage}
\makerunningwidth{mainpage}{\headwidth}
\makeheadposition{mainpage}{}{}{}{}
\makepsmarks{mainpage}{%
\nouppercaseheads
\makeoddhead{mainpage}{\rput[tl]{0}(0,0){Hello}}{}{}
\makeoddfoot{mainpage}{}{}{}
\makeevenhead{mainpage}{}{}{}
\makeevenfoot{mainpage}{}{}{}
}
\pagestyle{mainpage}

\begin{document}
Testing document
\end{document} 

In the MWE above, the command \rput from PSTricks is used only to type the top left-hand corner of the box containing the header text ("Hello") on the header baseline.

Answer 1

You can't set the head height to zero, since TeX wants to put something in it which will never fit. Your option here would be to set a regular, acceptable head height (of height \baselineskip, say) and raise the elements into position. This is achievable via

\documentclass[11pt]{memoir}% http://ctan.org/pkg/memoir
\usepackage{showframe}% http://ctan.org/pkg/showframe

\setstocksize{20cm}{20cm}
\settrimmedsize{\stockheight}{\stockwidth}{*}
\setlrmarginsandblock{.1\paperwidth}{*}{1}
\setulmarginsandblock{4\baselineskip}{3\baselineskip}{*}  
\setheadfoot{\baselineskip}{3\baselineskip}
\setheaderspaces{0pt}{*}{*}
\checkandfixthelayout

\makepagestyle{mainpage}
\makerunningwidth{mainpage}{\headwidth}
\makeheadposition{mainpage}{}{}{}{}
\makepsmarks{mainpage}{%
  \nouppercaseheads
  \makeoddhead{mainpage}{Hello}{}{}
  \makeoddfoot{mainpage}{}{}{}
  \makeevenhead{mainpage}{}{}{}
  \makeevenfoot{mainpage}{}{}{}
}
\pagestyle{mainpage}

\begin{document}
Testing document
\end{document}

Of course, you can replace Hello with \raisebox{\baselineskip}[0pt][0pt]{<stuff>} to raise the contents yet add to vertical height.